Understanding Reaction Dynamics in Coordination Chemistry—Application of High Pressure Techniques

In order to understand the dynamics of chemical reactions in general, detailed information on electronic, structural and kinetic properties is required. The key questions on how chemical reactions actually occur can in many cases only be answered in terms of information obtained from kinetic studies. In conventional kinetic studies of chemical reactions in solution, the variables usually selected include concentration, acidity, solvent, and temperature. In recent years, pressure has become an additional selected variable in such studies. It enables the measurement of the volume of activation and the construction of reaction volume profiles and thus assists in the elucidation of the underlying mechanism; it also completes the comprehension of reaction kinetics by adding another kinetic parameter that the suggested reaction mechanism must account for. Furthermore, the volume of activation is the only transition state property that can be correlated with the corresponding ground state property in an experimentally simple manner. In this paper, the insights so gained in our understanding of the dynamics of reactions involving coordination complexes will be presented. Such reactions are of fundamental interest to chemists since they often form the basis of catalytic, biological, environmental and energy related processes. Any additional information that will add to the understanding of the reaction dynamics is therefore of exceptional importance.     

Determination of inorganic sulphate in plasma by reversed-phase chromatography using ultraviolet detection and its application to plasma samples of patients receiving different types of haemodialysis

The determination of sulphate in plasma is described, making use of reversed-phase high-performance liquid chromatography with ultraviolet detection. The concentration of inorganic sulphate determined in plasma of twenty healthy volunteers was 0.307 +/- 0.092 mmol/l (mean +/- S.D.). In one stable chronic dialysis patient the kinetics of plasma sulphate removal were monitored during and after one single pass dialysis. In addition, plasma sulphate concentrations were determined in three stable chronic dialysis patients during a consecutive scheme of two single pass dialyses, five Redy dialyses and three single pass dialyses. As expected, plasma sulphate accumulates in plasma to a high steady-state level under Redy dialysis, whereas during single pass dialysis sulphate is efficiently removed.     

Separation of iron-52 from chromium cyclotron targets on the 2% cross-linked anion-exchange resin AG1-X2 in hydrochloric acid

Iron-52 can be separated from solutions of chromium cyclotron targets by eluting chromium, copper and radioactive impurities with 9.0M hydrochloric acid from a column containing 1.0 g of AG1-X2 anion-exchange resin. Iron-52 is retained and can then be eluted with 6.0M hydrochloric acid containing 0.05M hydrogen iodide or 0.05M sodium iodide. The separations are sharp and quantitative. Less than 2 microg of chromium will remain with the iron-52, from 2.0 g originally present.     

Serum estradiol measurement by solid-phase chemiluminescence immunoassay and direct radioimmunoassay

Estradiol017β is determined in serum extracts by solid-phase chemiluminescence immunoassay. The results are compared with those obtained from unextracted serum in routine conditions with a commercial radioimmunoassay (r.i.a.) kit. For the chemiluminescence procedure, a purified monoclonal antibody to estradiol-6-carboxymethyloxime/bovine serum albumin and the homologous chemiluminescent marker conjugate estradiol-6-carboxymethyloxime aminobutylethylisoluminol are used. Bound and free ligand are separated by washing and simple centrifugation. Results obtained by the chemiluminescence assay (y) and by r.i.a. (x) on 170 serum specimens from women during ovulation induction showed good correlation (y = 1.01x ? 16 with r = 0.95). The methods are similar in selectivity, detection limit (ca. 10 ng l^?1) and precision (interassay relative standard deviation, 8–13%).     

Rapid extraction and sample clean-up for the fluorescence densitometric determination of aflatoxin M1 in milk and mil powder

The diluted sample is passed through a SepPak C18 cartridge and the toxin is eluted with acetonitrile/water (3:7, v/v). The extract is cleaned up on a SepPak silica cartridge. The antidiagonal spot application technique is used for two-dimensional thin-layer chromatography. Spots are quantified by fluorescence densitometry. Recoveries of aflatoxin M1 added in the range 0.03-0.1 ng g^?1 of milk are 86–97%. The detection limit is about 0.005 ng g^?1 for milk and 0.05 ng g^?1 for milk powder.     

The diazo route to 2-vinylcyclopropylidenes

2-Vinylcyclopropylidene(2),3-methyl-2-vinylcyclopropylidenes(79,81)and2-(1-propenyl)cyclopropylidenes (95,97) were generated from the corresponding nitrosoureas in methanol at room temperature. The diazo route is initiated by the formation of 2-vinylcyclopropanediazonium ions (e.g.43) which do not undergo 1,3-carbon shifts. No cyclopentenyl products were found in weakly basic methanol where the diazonium ions prevail. Ring opening of the diazonium ions gives pentadienyl cations and products derived therefrom. Delocalisation of the pentadienyl cations was demonstrated by the distribution of deuterium and methyl labels. In the presence of strong base, 1-diazo-2-vinylcyclopropanes (e.g.48) arise by deprotonation of the diazonium ions. Rearrangement of 48 was excluded by independent generation of the potential product, 4-diazocyclopentene (103). Substantial quantities of 3-methoxycyclopentene (108) were obtained from 103, but not from 48. The 2-vinylcyclopropylidenes 2,79 and 95, arising by loss of nitrogen from the corresponding diazo compounds, undergo allene formation and Skattebøl rearrangement competitively. Cis-oriented methyl groups at either C-2(81) or C-2'(97) prevent the Skattebøl rearrangement. The cyclopentenylidenes 3 and 83 yield 4-methoxycyclopentenes (52,86) in excess over cyclopentadiens (4,84). In the presence of methyl vinyl ether, cycloaddition of 3 and electrophilic addition of 3-cyclopentenyl cation (51) occurred in a 1:14 ratio. Stereospecific formation of 52 indicates protonation of a ‘foiled carbene’ (3a) to give a bishomocyclopropenyl ion (51a). Our studies confirm that the various routes to 2-vinylcyclopropylidenes converge at the carbene stage.     

Light-Sensitive Phenacyl Crosslinked Dextran Hydrogels for Controlled Delivery**

Stimuli-responsive soft materials enable controlled release of loaded drug molecules and biomolecules. Controlled release of potent chemotherapeutic or immunotherapeutic agents is crucial to reduce unwanted side effects. In an effort to develop controlled release strategies that can be triggered by using Cerenkov luminescence, we have developed polymer hydrogels that can release bovine serum albumin and immunoglobulin G by using light (254 nm–375 nm) as a trigger. We describe the synthesis and photochemical characterization of two light sensitive phenacyl bis-azide crosslinkers that are used to prepare transparent self-supporting hydrogel patches. One crosslinker was designed to optimize the overlap with the Cerenkov luminescence emission window, bearing an π-extended phenacyl core, resulting in a high quantum yield (14 %) of photocleavage when irradiated with 375 nm light. We used the extended phenacyl crosslinker for the preparation of protein-loaded dextran hydrogel patches, which showed efficient and selective dosed release of bovine serum albumin or immunoglobulin G after irradiation with 375 nm light. Cerenkov-triggered release is as yet inconclusive due to unexpected side-reactivity. Based on the high quantum yield, efficient release and large overlap with the Cerenkov window, we envision application of these photosensitive soft materials in radiation targeted drug release.     

Incommensurate Phase in Λ-cobalt (III) Sepulchrate Trinitrate Governed by Highly Competitive N−H⋅⋅⋅O and C−H⋅⋅⋅O Hydrogen Bond Networks**

Phase transitions in molecular crystals are often determined by intermolecular interactions. The cage complex of [Co(C₁₂H₃₀N₈)]³⁺ ⋅ 3 NO₃⁻ is reported to undergo a disorder-order phase transition at T_c1 ≈133 K upon cooling. Temperature-dependent neutron and synchrotron diffraction experiments revealed satellite reflections in addition to main reflections in the diffraction patterns below T_c1. The modulation wave vector varies as function of temperature and locks in at T_c3≈98 K. Here, we demonstrate that the crystal symmetry lowers from hexagonal to monoclinic in the incommensurately modulated phases in T_c1<T<T_c3. Distinctive levels of competitions: trade-off between longer N−H⋅⋅⋅O and shorter C−H⋅⋅⋅O hydrogen bonds; steric constraints to dense C−H⋅⋅⋅O bonds give rise to pronounced modulation of the basic structure. Severely frustrated crystal packing in the incommensurate phase is precursor to optimal balance of intermolecular interactions in the lock-in phase.